1. Field of the Invention
The present invention relates generally to a disk for recording information. More specifically, the invention relates to a disk with a recording medium sheet attached on a disk base. Further particularly, the invention relates to a structure of bonding the recording medium sheet onto a disk base.
2. Description of the Background Art
A conventional disk of this type has been disclosed in U.S. Pat. No. 4,631,609, issued on Nov. 18, 1986. The prior proposed disk comprises an essentially disk-shaped or thin dish-shaped disk base having a center hub. The disk base has a circumferential edge section axially offset from the general surface of disk base for defining therebetween an annular groove. The inner edge portion of the circumferential edge section is oriented on the plane to locate a recording medium sheet. From this inner edge portion, is extend a tapered surface. The tapered surface serves as bonding surface for bonding the recording medium sheet onto the disk base with a predetermined magnitude of radial tension so that the recording medium sheet can be stretched over the annular groove between the center hub and the inner edge portion of the circumferential edge section.
In manufacture, the recording medium sheet is carried by a device or machine adapting to provide the predetermined radial tension. Bond is applied to the tapered surface for bonding the circumferential portion of the recording medium sheet thereonto. After bonding, the circumferential edge portion extending from the outer circumference of the disk base is cut and removed.
During the aforementioned process for manufacturing, the recording medium sheet can slidingly move on the bonding surface, thereby rupturing the bound. As a result, bonding force at various circumferential positions of the recording medium sheet becomes uneven. In the worse case, part of the recording medium sheet can be peeled off at a portion where the most bond is removed by the recording medium sheet slipping thereon. Since the radial tension force is applied in radially outward direction, the bond removed from the bonding surface can be accumulated essentially along the outer circumference of the disk base. Such accumulated bond tends to cause difficulty in cutting off the extra portion extending out of the circumference of the disk base.
For preventing this, the aforementioned prior proposal forms a groove at the intersection between the surface defining the plate for installing the recording medium sheet and the bonding surface. The groove is intended to maintain the recording medium sheet oriented at the corresponding portion away from the surface of the disk base so that the recording medium sheet can on the bond on the bonding surface for eliminating or at least reducing bond scrape from the bonding surface. However, in the prior proposal the bonding surface has essentially the same gradient as the sheet installing surface. The bond on the bonding surface may be placed above a plane on which the installing surface and the bonding surface lie. Therefore, the recording medium sheet still serves for scraping the bonding from the bonding surface.